For processing video signals different types of filters are known. Often used are filters wherein different numbers of samples or pixels respectively form a filter window. In linear filters the value of these samples are evaluated by filter coefficients and added. The samples can be taken from one line or different lines within the same frame. Such filters are called spatial filters. Temporal filters use samples from different frames. Linear filters can be FIR filters (finite response filters) or recursive filters.
A further group of filters comprises non-linear filters whereby the combination of the values of the samples is not performed by a linear operation. One of these filters is the median filter, which outputs the value which ranks in the middle of all values in the window. Other non-linear filters produce the maximum or the minimum value or non-linear combinations of values covered by the window.
The known filters have different properties and are used for different purposes. Besides the property, which is used for a special purpose other properties of the same filter may cause disturbances. E.g. FIR filters can be used as low-pass filter without generating alias frequencies. However they introduce a certain rise time to edges, so sharp transitions will be blurred.